Such a laser is known from U.S. Pat. No. 4,864,578. That laser, however, is a continuous mode dye laser having a bandwidth of 1 MHz. The instant invention, on the other hand, is used preferably with pulsed lasers having a bandwith of 1.2 GHz, in other words three orders of magnitude bigger.
DD 228 117 A1 discloses a resonator arrangement for a tunable laser comprising a single reflecting structural element of such design that good spectral filtering is obtained at high wavelength selectivity and narrow line width. The tuning of the wavelength is continuous and effected by means of pressure variation. The laser beam is expanded by a system of prisms.
A paper by R. Konig, S. Mory, and A. Rosenfeld published in J.Phys.E.: Sci.Instrum. 20 (1987), pages 200-203.describes a pulsed dye laser with which the beam is expanded in the resonator by means of prisms and the wavelength is tuned by turning a grating and/or an FP etalon.
A pulsed dye laser adapted to be tuned in a wide range of wavelengths by means of an FP etalon and a grating is known also from the paper by Olcay, M. R. et al. "Tuning of a narrow linewidth pulsed dye laser with a Fabry-Perot and diffraction grating over a large wavelength range" published in Applied Optics, vol.24, 1985, no. 19, pages 3146-3150.
DE 37 44 323 Al discloses a laser with which stabilization of the frequency o the laser beam is achieved by inputting part thereof into a Fabry-Perot interferometer so as to derive an adjustment signal for the setting of a wavelength selective member. The ring system of the Fabry-Perot interferometer is imaged on a beam position photosensor such as an adjacent pair of photo diodes so that it may be compared with a memorized reference signal so that a setting signal may be obtained for adjustment of the wavelength selective member of the laser.
The instant invention starts from a different problem than stabilizing the frequency of a laser beam.
It is known to narrow down the line or bandwidth of a pulsed laser, especially a dye laser, by providing an etalon in the laser resonator in addition to the tuning grating of the laser. The etalon considerably reduces the bandwidth of the laser beam because of its selective transmission properties. For tuning such a laser, the grating and the etalon must be synchronized. These two wavelength selective members (etalon and grating) must be positioned with respect to each other in such manner that the transmission of the etalon will correspond to the wavelength which is given by the grating. The etalon may be replaced by other wavelength selective means, such as a Fabry-Perot interferometer, double refractive crystals, and the like.
When an etalon is applied, the alignment of the etalon with the grating is accomplished by slightly tilting the etalon with respect to the laser beam axis.
Now, if the wavelength of the laser is to be tuned (varied) both the grating and the etalon located inside the resonant cavity (so-called intracavity etalon) must be tilted in synchronism. It is the difficulties encountered with such synchronous adjustments of wavelength selective members (e.g. grating and etalon) that the instant invention is directed to.
With the state of the art, continuous tuning of the laser wavelength can be effected only in a very limited range of approximately 1 nm due to the fact that so-called walk-off losses caused by the etalon in the resonant cavity occur when the grating and etalon are moved in synchronism. Furthermore, the minutest deviations from linearity of the grating and etalon drive will result in desynchronization so that, in the extreme, the laser will start to oscillate simultaneously at two adjacent transmission wavelength of the etalon.